The goal of this proposal is to construct a vaccine that is broadly protective against the epidemiologically most important Shigella serotypes and toxin and colonization factor types of enterotoxigenic E. coli (ETEC), two enteropathogens of substantial public health importance to the U.S. and global populations. Both pathogens are designated serious threats by the Centers for Disease Control (CDC) in the U.S. due to increasing multidrug resistance leading to fewer options for therapeutic intervention. Shigella and ETEC readily acquire antimicrobial resistance mechanisms and additional virulence factors, making these pathogens important emerging threats. An oral vaccine with broad coverage against the most prevalent circulating isolates would be beneficial to multiple populations, including: 1) adult and child travelers who visit less developed countries where these infections are hyperendemic; 2) children and adults in certain high risk populations in the US; 3) children < age 5 years in developing countries, and 4) for mass immunization to control natural or deliberate outbreaks. The vaccine will consist of a mixed inoculum of 6 live attenuated strains of Shigella expressing ETEC colonization factor antigens and antigens to induce toxin neutralizing antibodies against heat labile (LT) and heat stable (ST) toxins. Oral immunization is an effective method for inducing mucosal as well as systemic immune responses believed to be important in protection against these enteropathogens and oral delivery is a practical route for product deployment and for enhancing compliance. We are taking advantage of the successful completion of five attenuated Shigella vaccine strains expressing heterologous antigens during the previous CETR funding period, and using current epidemiological data, as well as novel technological advances, to improve and broaden the vaccine formulation in order to maximize the protective efficacy of this Shigella-ETEC vaccine product and optimize features for production. Our specific objective is to complete vaccine candidate optimization and pre- clinical evaluation to enable IND submission for advancement to clinical trials. This project relates directly to the overarching goal of this Program to develop active vaccination and passive antibody strategies to prevent disease caused by multidrug-resistant bacterial pathogens. The collective expertise provided by CETR project investigators and collaborating scientists along with the Center for Vaccine Development's experience in translating products through manufacture and clinical evaluation, will accelerate efforts to advance vaccine development.